High altitude syndrome
-
Upload
sand-whale -
Category
Documents
-
view
46.813 -
download
4
description
Transcript of High altitude syndrome
High altitude medical problem
ดอยลั�งกาหลัวง 2,031m
ภู�สอยดาว 2,102 m
ดอยหลัวงเชี�ยงดาว2,195 m
ดอยผ้�าห�มปก 2,285 m
Altitude Height Effect
Intermediate altitude
1520 - 2440 m (5000 - 8000 ft)
exercise performance alveolar ventilation↔arterial oxygen transport
High altitude >2440 m (>8000 ft) AMS
Very high altitude
4270 - 5490 m (14,000 - 18,000 ft)
AMS
PATHOPHYSIOLOGY
ventilation
• PaO2 carotid body& respiratory center
ventilation PaCO2
Performance
Chronic hypoxiaSedative agentDuring sleep
ventilatory acclimatization
ventilation
pH (respi alkalosis)
HCO3 excrete via kidney
pH return to normal
Acetazolamide
Blood
• EPO w/in 2 hr • Rbc mass w/in
days to wks• if excessive
chronic polycythemia
Fluid Balance
• Reset Osm stat: plasma volume and hyperosmolality (s osm290 - 300)
• diuresis and hemoconcentration :healthy response• Antidiuresis is a hallmark of AMS
Peripheral venous constriction
in central blood
volume
ADH &aldosterone
diuresis
Cardiovascular System
CO = SV HR
Pulm.vasoconstriction pulm.pressure
Cerebral blood volume O2 to brain ICP
Exercise capacity
• measured by VO2max, drops dramatically on ascent to altitude
• During acclimatization, submaximal endurance after 10 days
Sleep at High Altitude
• Sleep stages III and IV ↓ stage I frequent arousals (improve with time at altitude)
• Cheyne-Stokes respiration in those sleeping at >2700 m (>8860 ft)
• the frequent awakenings & periodic breathing not related to AMS
• mechanism of the lighter sleep →cerebral hypoxia. • Quality of sleep and arterial oxygenation during
sleep improve with acclimatization and with acetazolamide
HIGH-ALTITUDE SYNDROMES
High altitude syndrome
• Acute hypoxia• Acute mountain sickness• High-Altitude cerebral edema• High-Altitude pulmonary edema• Peripheral edema• High-altitude retinopathy• High-altitude pharyngitis and bronchitis• Chronic mountain polycythemia• UV keratoconjunctivitis
Acute hypoxia
• occurs in the setting of sudden and severe• Unacclimatized persons become unconscious
at SaO2 50 - 60%, PaO2 < 30 mm Hg, or a jugular venous PO2 of <15 mm Hg
• immediate administration of oxygen, rapid descent
Acute Mountain Sickness
• setting of more gradual and less severe hypoxic
• characterized by headache, GI disturbances, dizziness or light-headedness, and sleep disturbance
What’re factors determine individual susceptibility to AMS ?
• Age • Sex • Body weight • physical fitness
Pathophysiology
• renin-angiotensin aldosterone ADH
The cerebral edema, interstitial pulmonary edema, peripheral edema, and antidiuresis
Clinical feature
• mild : alcohol hangover• Headaches : bifrontal and worsen with
bending over or performing a Valsalva maneuver
• GI symptoms : anorexia, N/V• irritable & wants to be left alone• Sleepiness • deep inner chill also are common
Clinical feature
• rapid ascent of an unacclimatized person to ≥2000 m
• Symptoms develop between 1 -6 hours later, but sometimes are delayed for 1 - 2 days
Severe headache vomiting oliguria Ataxia
and AOC HACE
Physical examination
• percent SaO2 overall correlates poorly with the diagnosis of AMS
• postural hypotension may be present• Localized rales ≥ 20%• Funduscopy :tortuosity and dilatation, and
retinal hemorrhages (at altitudes >5000 m)• facial and peripheral edema is a hallmark
The goals of treatment are to
prevent progression
abort the illness
improve acclimatization
3 principles of Rx
(1) do not proceed to a higher sleeping altitude in the presence of symptoms
(2) descend if symptoms do not abate or become worse despite treatment
(3) descend and treat immediately in the presence of a change in consciousness, ataxia, or pulmonary edema
Treatment
• Oxygen effectively relieves symptoms, but it is generally unavailable in the field or reserved for those with moderate to severe AMS
Medication
Indications for acetazolamide (1) a history of altitude illness(2) abrupt ascent to >3000 m (>9840 ft)(3) AMS requiring treatment(4) bothersome periodic breathing during sleep
Symptomatic treatment of AMS
• Headache :aspirin, acetaminophen or ibuprofen
• N/V: ondansetron• f/q wakening: zolpidem,diphenhydramine
Prevention
• Graded ascent with adequate time for acclimatization is the best prevention
• Prophylactic acetazolamide – started 24 hr before the ascent – continued for the first 2 days at altitude– restarted if illness develops
HACE
• HACE : progressive neurologic deterioration in someone with AMS or HAPE
• altered mental status, ataxia, stupor, and progression to coma if untreated
• severe, diffuse cerebral edema with multiple small hemorrhages and sometimes thrombosis
Treatment of HACE
• oxygen supplementation• descent(the highest priority)• steroid therapy• acetazolamide may be used as an adjunct
MRI findings reversible white matter edema evidenced byT2 signal, esp.in the splenium
of the corpus callosum
HAPE
• most lethal of the altitude illnesses• easily reversible with descent and oxygen
administration• Risk factors:heavy exertion, rapid ascent, cold,
excessive salt ingestion, use of a sleeping medication
Pathophysiology
• HAPE is a noncardiogenic, hydrostatic edema• The culprit in HAPE is high microvascular
pressure Pulmonary hypertension
Clinical
• Early diagnosis is critical, exercise performance & dry cough are enough to raise the suspicion of early HAPE
• The condition typically worsens at night • Low-grade fever is common, and tachycardia
and tachypnea• SO2 low for altitude
Chest radiographic
progress from interstitial localized alveolar generalized alveolar infiltrates
Treatment
• The key to successful Rx : early recognition, early stage is easily reversible
• Immediate descent is the Rx of choice, but this is not always possible
• The optimal therapy depends on – the environmental setting, – evacuation options– availability of oxygen or hyperbaric units– ease of descent
Portable hyperbaric bag
medication
• Because oxygen and descent are so effective, experience with drugs has been limited
• nifedipine, phosphodiesterase 5 inhibitors:sildenafil and tadalafil
Other high altitude medical problem
• Peripheral edema• High-altitude retinopathy• High-altitude pharyngitis and bronchitis• UV keratoconjunctivitis
Special population
• Patients who have hypoxic cardiovascular and pulmonary diseases such as COPD or CHF , CAD, pregnant